Resistor winding



July 13, 1954 H. E. LENsE 2,683,567

RESISTOR WINDING Filed Deo. 19, 1949 2 Sheets-Sheet l 34 avr/P01,

Minnow 34 5 July 13, 1954 H. E. LENsE 2,683,567

RESISTOR WINDING Filed De0- 19, 1949 2 Sheets-Sheet 2 JNVENTOR.

Patented July 13, 1954 RESISTOR WINDING Herbert E. Lense, Berwyn, Ill., assignor to David T. Siegel, Glencoe, Ill.

Application December 19, 1949, Serial No. 133,917

6 Claims.

This invention relates to the manufacture of resistors, and concerns more particularly the accurate predeterminaticn of the resistance value in resistors of the wire wound type in connection with the winding thereof.

Resistors in general fall into several classes of accuracy. In many installations the use of wire wound resistors is indicated, but such resistors as conventionally manufactured frequently do not possess the degree of accuracy required. Wire Wound resistors are usually manufactured by Winding resistance wire on a core of insulating material which is generally ceramic. If a resister is manufactured and then its resistance checked, the process is tedious and is not well adapted to mass production methods. Furthermore, the resistance is then fixed and there is nothing that can be done if it is not of the proper value.

It is possible to predetermine the resistance of a wire wound resistor with some degree of accuracy by counting the number of turns applied, When the core diameter and the resistance of the wire per unit of length is known. Such a method is, however, undesirable for if the core is of irregular diameter, the length for a given number of turns cannot be accurately forecast. The tension under which the wire is wound on the core will determine the tightness of the winding and hence the total length, and as the tension may vary from time to time, another unpredictable factor is introduced. Excessive tension may even stretch the wire somewhat and hence change its diameter and consequently its resistivity. Even if the wire is not stretched by excessive tension, the diameter, the

shape of the cross section, the composition and the consequent resistivity of any commercially available wire may vary sufliciently from point to point to introduce a considerable error in the resistance desired.

A more accurate method would perhaps be to measure the actual length of the wire wound on the core rather than the number of turns. This would eliminate any errors due to irregular core diameter cr tightness cf winding, but errors would still be introduced due to the variations in the gauge of the wire, in the cross section and in the composition of the wire, and in any stretching caused by excessive tension.

In accordance with the present invention, the resistance value of the resistor is measured, accurately, during the wire Winding operation, and the operation automatically terminated when the desired resistance value is reached.

A principal object of this invention is the provision of an improved resistor and of apparatus and methods for making such a resistor.

A more specic object is the provision of means and methods for manufacturing a wire wound resistor of the desired resistance, in which the resistance of the resistor is measured during its manufacture.

An additional object of the invention is to provide means and methods for making a resistor as outlined above, in which the resistance is measured with apparatus of high sensitivity.

A further object of the invention is the provision of resistance measuring control means which have very rapid action at the cut-oli point when the desired resistance is reached.

Yet another object of the present invention is the provision of resistance measuring control means which are largely immune from transitory variations in the resistance value.

Other and further objects and advantages of this invention will be apparent from a perusal of the following description when taken in conjunction with the accompanying drawings in which:

Fig. 1 is a perspective View of a precision resistor produced by my means and methods;

Fig. 2 diagrammatically indicates apparatus capable of carrying out my invention;

Fig. 3 is a block diagram of the electrical control circuit associated with the apparatus of Fig. 2; and

Fig. 4 is a schematic diagram of the electrical circuit.

Generally, to carry out my invention, I plan to utilize a wire winding machine similar to that disclosed by H. Chanowitz in his Patent No. 2,460,807, issued February 8, 1949. A terminal lug from which the Wire is wound is grounded to the machine and the distributing lead screw is insulated. A Wheatstone bridge, in conjunction with an amplifying system of novel construction, is utilized to measure the resistance of the wire between the lead screw and the ground connection and to automatically shut off the driving motor when a predetermined resistance has been reached. The length of wire between the resistor and the lead screw will be a constant for each winding operation and introduces no error. Indeed, if desired, the time lag between the breaking of the motor` circuit and the stopping of the machinery may be adjusted to wind the length of wire between the lead screw and resistor onto the resistor core. The electrical circuit is so designed that transitory varia- 3 tions in resistance value, such as for example the catching of a piece of dust on the lead screw, do not shut off the machine.

Referring more particularly to the figures, there is illustrated in Fig. 1 a precision resistor comprising a ceramic core 6 having lugs 8 and I adjacent each end and resistance wire i2 coiled about the core therebetween. The wire may be secured to the lugs by any desirable means, such as soldering or welding, the latter being disclosed in the aforementioned Chanowitz patent.

As illustrated in Fig. 2, the core 6 may be mounted on a winding spindle I4 for the application of the wire. A compression spring i6 is mounted about the spindle abutting a collar IS and the core is screwed up against the spring by means of a nut 20. A terminal clamp 22, mounted on the collar I8, clampingly engages one of the lugs 8 to ground it to the spindle |4, and hence to the frame 24 of the winding machine on which the spindle is mounted. The spindle is driven by means such as a belt 26 engaging a pulley 28 on the spindle and a pulley 30 on the shaft of a motor 32. The motor 32 is powered by leads 38 from a control box 34 having a motor start switch 36 and A. C. input leads 60. A connection 40 is provided between the frame 24 and the control box.

A second pulley 42 is mounted on the spindle |4 and is engaged by a belt 44 to drive a pulley 46. On the same shaft with the pulley 46 is a gear 43 which may drive an idler gear 50 to drive an insulating fiber gear 52 which is mounted on the shaft 54 of a lead screw 56. The shaft 54 is journaled in an insulated frame 58 and a brush 60 which is mounted Aon the insulated frame engages a slip ring 62 on the lead screw shaft. The wire I2 being wound on the core 6 is supplied from a supply spool 64 and engages the threads of the lead screw 56 in order to be advanced along the core 6. An electrical connection 66 is provided between the brush 60 and the control box 34.

As shown in a block diagram of Fig. 3, the power line 68 is connected to a transformer 10 which supplies power to a Wheatstone bridge 12. The lead lines from the top of the bridge lead to the frame and `brush and are the same as the lines "i0 and 66 in Fig. 2. The bridge feeds a three-stage amplifier 14 which amplies the A. C. signal from the bridge and feeds it onto a signal rectifier '16. The amplifier 14 vis provided with power from a power supply 18 connected to the power line 68. A rectier 80 receives A. C. power from a transformer B2 which is connected to the power line 66 and supplies D. C. power through a motor control relay coil 04 to a thyratron shut-off tube 86 which is controlled by the D. C. output of the rectifier T6. rIhe motor control relay coil is connected in series with the motor control switch 36 previously mentioned, and acts to open a motor switch 88 in series with the motor 32 in its connection to the power line 68.

In Fig. 4 is shown a detailed schematic diagram of the control apparatus shown in Fig. 3. The power line 68 may be provided with a master switch 90 and a circuit breaker or fuse 92. The transformer is connected directly to one lapex 94 of the Wheatstone bridge 12. The transformer is also connected through a lcurrent limiting resistor 96 and normally closed relay contacts 98, actuated by the motor control relay 64 to the opposite apex |00 of the bridge. The apex |00 actually constitutes a slidable tap ori a single resistor, but this is electrically the equivalent of the conventional form of Wheatstone bridge, and it is more convenient. rAnother apex |02 of the bridge is grounded and is connected to the lead wire 40 from the grounded winding machine frame. The other lead wire 66 is connected to the apex 94 so that the arm between the apices 24 and |02 is the unknown arm of the bridge. The heretofore unreferred to apex |04 is connected by an adjustable arm on a resistor |05 to apex 94 and is connected to a voltage divider network comprising resistors |06 and |08. A capacitor ||0 is connected in parallel with the resistors |06, |00 to remove high frequencies from the signal, and the junction between the resistors |06 and |08 is connected to the control grid of an amplifying tube ||2. rIhe amplifying tube is preferably of the multigrid type in order to provide high amplification. The cathode of the tube ||2 is provided with cathode bias by the usual resistor-capacitor combination ||4 which is grounded through a resistor ||6. The output of the tube ||2 is connected by means of a conventional coupling network ||8 to the grid of a second amplifier tube |20, which is also preferably of the multigrid type and is cathode biassed by the usual resistor-capacitor combination |22. The output of the tube |20 is fed by means of a conventional coupling network |24 to the control grid of a third amplier tube |26. This tube is also provided with cathode bias by means of the usual resistor-capacitor combination |20 which is grounded through the previously mentioned resistor I I6. The common cathode or ground resistor ||6 of the tubes ||2 and |26 provides inverse feedback in order to minimize changes in line voltage, tube parameters, etc., and to provide a certain amount of limiting action.

The power supply 1f-8 previously referred to comprises a conventional transformer |30 and full wave rectifier |32 feeding through a fuse |34 to a filter network |36. 'Ihe third amplifier tube |26 is supplied with power through a plate load resistor |68 and an inductance |40 from a point |42 on the filter. The same point |42 is connected through a resistor |44 to a voltage regulating network |46 including voltage regulator tubes |46. From one point |50 on the regulating network, plate power is supplied to the tubes ||2 and |20 through decoupling networks |52 and |54, and from the same point screen grid potential is supplied to the tubes ||2 and |20 through decoupling networks |56 and |58. Screen grid potential is supplied to the tube |26 through a resistor |60 connected to another point |62 on the lter |36.

The output of the tube |26 is shunted by a capacitor |64 of low value, and the plate of tube |26 is connected through a `coupling capacitor |66 to a diode signal rectifier |68. The rectier |68 is connected as a full wave rectifier with the cathodes connected together through a load resistor |10 to the junction of a pair of resistors |12 and |14 connected in series across the output of the tube |26. A capacitor |16 of rather large size is connected in parallel with the load resistor' |20 so that the potential thereacross will not vary too rapidly and the circuit will not respond to transitory variations in resistance. A tap on the resistor |10 is connected to the control grid of a thyratron regulator |18 and is adjustable to compensate for individual differences between thyratrons. The cathode of the control tube .fit is connected to one arm of the power transformer 82 and is also connected to one end of a load resistor |80 of a thyratron |82 diodeconnected as a gas filled rectifier. The anode of the rectifier |62 is connected through a delay relay i8@ to the other end of the arm of the transformer S2 to which the cathode of the control tube H8 is connected. The delay relay prevents the application of plate potential to the rectier |82 until such time as the filaments have heated. The resistor |80 is paralleled by 'a capacitor |86 to constitute a lter, and has connected in parallel with it the series combination of the motor relay coil S4 and the motor control switch 3S. The relay coil 84 is paralleled by an indicator tube |88 in series with a resistor |90. The normally closed switch 8B associated with the relay coil 84 is connected in series with the motor 32 and connected across the power line 63 as previously noted.

To initiate a winding cycle, the operator momentarily opens the normally closed starting switch Se, which deenergizes relay coil |84, permitting switches 8&3 and 98 to close to apply current to the winding motor 32 and to the control bridge circuit. At the start of any winding cycle the Wheatstone bridge is badly out of balance. This causes a relatively large potential to be applied to the grid of the i-lrst amplifier tube |2 and results in a large negative bias on the control tube iit. rthe control tube |18 is thus cut on and no current is carried by the relay coil 84 even after the switch 36 is permitted to close. The amount of unbalance at the start would be suiiicient to ruin a galvanometer of appreciable sensitivity such as is usually used in conjunction with a Wheatstone bridge, but in the circuit illustrated, there is a limiting and clipping action provided by the ampliiier circuit, so as to keep the negative voltage applied to the grid of the control tube |18 from exceeding a reasonable value. Within large limits, however, it makes very little difference what negative voltage is applied to the grid of the control tube |18, so long as the grid is maintained below cut-01T.

As the wire winds onto the core 6 the resistance across the unknown arm of the Wheatstone bridge increases, and the amount of unbalance decreaes so that a lesser signal is fed to the control grid of the ampliiier tube 2. With the lesser input, the limiting action is less severe with the result that the change of potential on the grid of the control tube 1t is not proportional to the change on the bridge unbalance. The capacitor |16 is sufliciently large that transitory variations in resistance and in the consequent unbalance or" the bridge do not cause the control tube |18 to re.

As the resistance wound on the core 6 nears the correct value, the unbalance on the bridge becomes much less and the grid of the control tube H8 approaches firing potential. At the precise moment that balance is reached on the bridge there is no input to the first amplifier tube ||2 and consequently no output from the rectier |68. As a result the control tube |18 res, and current is passed through the relay coil 8, which concurrently opens the motor circuit and removes the potential applied to the Wheatstone bridge. The winding operation stops at a predetermined point, and the wire may be welded to the second lug l@ and cut off as disclosed in the aforementioned Chanowitz patent, or it may be suitably secured to the lug in any other manner. During the securing and cutting operation and until the next resistor is started the resistance across the unknown arm of the Wheatstone bridge varies rapidly over wide limits, but this has no eiiect whatsoever, as there is no potential applied to the bridge at this time.

When it is desired to start another winding cycle, the motor `control switch 36 is pushed to open the plate circuit of the control tube |1'8 and stop the ow of Vcurrent through the relay 84. This allows the normally closed relay switches 88 and 98 to close and starts the motor 32 and again applies potential to the Wheatsone bridge 12. The Wheatstone bridge is, of course, at this time unbalanced and a negative output is supplied by the rectiiier |68 to bias the control tube |18 beyond cut-on so that the motor control switch 35 "may, be released and returned to its normally closed position.

It should now be apparent that I have presented means and methods for constructing wire wound resistors with a high degree of accuracy. Indeed, it has been' found that the resistor produced will be accurate to within one per cent, and less, o1 a desired value.

An important feature of the invention is the sensitivity 'of the control circuit at cut-ofi, as compared with its much less sensitivity at other times. As previously indicated, a galvanometer such asis usually used to indicate the balance of a bridge would be destroyed by the tremendous unbalance at the start of the winding operation, if the galvanometer were to be suiiiciently sensitive at the cut-ofi point. My amplifier' circuit is highly sensitive at cut-off, but limits the ampliii'cation of the unbalance when the unbalance is great, prior to the cut-oli point.

It is further to be noted that the control element is a thyratron tube which is not damaged by the application of a negative potential far beyond cut-01T. The circuit is rapid in its response at the precise moment of balance of the bridge, so that the control tube res to instantaneously stop the drive motor and remove potential from the Wheatstone bridge. While highly sensitive at cut-off, the operation of the circuit is not disturbed by transitory variations in the winding resistance value, due to dirt on the lead screw, or like matters.

A precision resistor wound in accordance with its actual desired resistance value, and measured thereby, is thus produced by means and methods which are well adapted to mass production methods.

The desired resistor value may be reset at any time by adjustment of the bridge leg |95, so that resistors of any desired resistance value may be made.

It is to be understood that my invention is not to be limited by the foregoing illustrative eX- ample, but only by the appended claims.

I claim:

l. Means for manufacturing resistors of the type having a resistive element wound on a nonconductive core comprising means for rotating said core, means for advancing said resistive elem-ent axially relative to said core, bridge balancing means, means for including the resistive element being wound on said core in one arm of said bridge balancing means, a `gas filled electron tube, means for developing a biasing potential in response to unbalance of said bridge means, said biasing potential normally rendering said gas filled electron tube nonconductive but dropping in response to balance of said bridge balancing means .to allow said gas filled electron tube to break down and become conductive, said last named means including means fer minimizing the eect of bridge unbalance on said electra!! tube when the unbalance is large and ineens. for maximizing the eiect when the unbalanoe is small, a relay coil in the plate circuit of said electron tube, means for applying potential t@ said bridge balancing means, including; normally closed switch contacts openable by said relay coil, and normally closed switch means operiabie by said relay coil for supplying Dctential to said driving means, both said switch contacts. land said switch means opening in response to conduction of said electron tube to remove potential from said bridge balancing means and from said dif-iv ing means.

2. Means for manufacturing resistors as defined in claim 1 in which means are-provided for dropping the plate potential of the gas filled electron tube to cut o said tube.

3. Means for making resistors comprising means for winding an elongated resistance elef ment onto a non-.conducting support, driving means for operating said winding means,y bridge balancing means, means for including the resistance of the resistance element being wound Qn the support in one arm of the bridge, am? pliier connected to the output .ef tbe bridge for developing a biasing potential in response to unbalance of the bridge, said ampliner limiting the biasing potential developed when the unbelf ance of the bridge is large, a gas lled tube naving its control electrode connected t0. Said anfiplier and controlled by the biasing potential to render the tube non-conductive when said d ge is unbalanced and conductive when said bridge is balanced, and control means in the` plate eircuit of said gas lled tube actuated by current in the plate circuit when said tube is rendered conductive to stop said driving means when the bridge is balanced.

4,. 1n apparatus for winding resistors, means for winding an elongated resistance element, driving means fer operating said Winding means, a bridge circuit including said resistance element in one arm thereof, potential applying means connected to said bridge, amplifier means cgnnected to said bridge circuit responsive to imbalance thereof for developing a biasing potential, substantially no biasing potential being develcped when said bridge is balanced, said ampliiier means including means for limiting the biasing potential when the unbalance of the bridge is large, a gas lled tube having its grid connected to said amplifier means and controlled by the biasing potential to render said tube nonconductive when said bridge is unbalanced and conductive when said bridge is balanced, and control means in the plate circuit of said gas filled tube actuated by current in said Plate circuit when said tube is rendered conductive to stop said driving means when said bridge is balanced.

5. In apparatus for Winding resistors as defined in claim 4, wherein said control means inludes a switch actuated when said gas lled tube is rendered conductive to disconnect said potential applying means from said bridge.

6. vIn apparatus for winding resistors as defined in claim 4, wherein a reactance element is connected to the grid of the gas lled tube to prevent transitory disturbances from rendering said tube conductive.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,977,697 Rockwood Oct. 23, 1934 2,199,603 Ackley May 7, 1940 2,319,413 Leathers et al May 18, 1943 

